Although simple plug tighteners are known which transmit limited torque in one direction, with such constructions the torque does not occur directly in the vicinity of the spark plug but rather is transmitted by a shaft or a permanently connected tightener. Because of the construction of many motors large spark plug tighteners with torque-limiting characteristics cannot be used, and thus the degree of tightening of the spark plugs in such motors is left for the most part to the judgment of the mechanic. Spark plugs, however, should be tightened with a definite torque, because only in this way can protection of the light metal housing of the motor block be guaranteed and the necessary electron gap of the spark plugs retained. Regardless of how much care may be given to the setting of the gap in the spark plugs, with the uncontrolled turning of the plugs during installation, the best preparations can be destroyed, because the separation between the electrodes can change with the applied force. It is also apparent that damage to the threads may occur, which could result in frequently having to replace the thread windings. The spark plug tightener of the present invention is designed to permit the spark plug to be secured with a determinable torque, and upon exceeding the set torque to release the plug, while permitting a higher torque to be applied to the plug in the reverse direction when it is desired to remove the plug.
The foregoing objectives are accomplished by the present invention by the housing and the turning shaft being provided with radially extending trapezoidally-formed depressions and elevations with steeply sloping sides, and with the housing having an inner set of teeth in which a ratchet engages for increasing the torque in the reverse direction, which ratchet is situated in the shaft extending through the housing.
In one embodiment of the present invention the inner teeth of the housing are tangentially oriented, and the ratchet is a key wich engages the inner teeth by means of a spring motion out of a cavity in the shaft.
In the spark plug tightener of the present invention, over-tightening cannot occur, with resulting damage to the threads, and the spark plug can be secured with the desired adjustable torque. As soon as the desired torque is attained, the noise of the depressions and elevations sliding over each other indicates to the mechanic that the installation of the spark plug is complete.
Another advantage of the present invention is that the construction of the tightener is very simple, and does not exceed the dimesnions of conventional spark plug tighteners. Thus, the tightener may be used in different arrangements with differently constructed types of spark plugs in different motors with the use of extensions. Because the torque is determinable, the threads are protected with the optimum compression.
Still further, the inner teeth acting together with the ratchet allows a such higher torque to be applied for unscrewing, which is often necessary for removing plugs. Tighteners with reverse ratchets are known; however, with such tighteners the reverse motion occurs without transmitting any torque.
Still further, the housing and the cover of the invention have a scale with which the torque of the spark plug tightener can be set.